This invention generally relates to an improved rubber compound, and more specifically relates to the improvement of the elastomeric components for tread pads of tracked vehicles, especially endless track military vehicles. Track laying vehicles wherein a continuous track is constantly laid down in the direction of movement of the associated vehicle are well known. Examples of such track laying devices are the military tanks and personnel carriers. Such devices have an endless track with a plurality of linked metal track shoes. These military tracked vehicles and other commercial type tracked vehicles are frequently equipped with rubber track pads, rubber blocks or endless-band rubber track to reduce shock, noise, wear and damage to road surfaces. These endless tracks render the vehicles operational in rough, uneven terrain when necessary under military maneuvers. The vehicles, however, also travel over roads and hard surfaces and therefore the elastomeric components of the endless tracks should be of the type that wears well under abrasive rough terrain conditions. One example of a suitable track laying structure is disclosed in U.S. Pat. No. 3,078,128 issued Feb. 19, 1963 to the United States of America. Examples of previous tank tread pads and related compositions are well defined in various other prior U.S. patents such as U.S. Pat. Nos. 3,781,067; 4,279,448; 4,587,280; 4,461,516; and 4,470,641.
Historically, field performance of these elastomeric track pad components has been poor, especially for the medium to heavy tonnage tracked vehicles, 40-60 tons. The service life of these tank pads is affected not only by the terrain and environmental conditions but also by the speed, cornering, braking, weight of the vehicle, and the track tread design. While the operational life of the metal components is approximately 5000 miles for vehicles of the 55 tons weight class, the average life of the rubber pads is seldom more than 1500 miles under the best circumstances, and is usually less than 500 miles under the severest conditions. The elastomeric components of an endless track are affected in several ways depending upon service. Directly, it can cause cuts, tears, chunking, blow-outs and abrasive wear. Indirectly, it causes damage through hysteretic heating, environment convection and surface/terrain heating. Those skilled in the art are aware of the types of failures on rubber tank track pads, road wheels and rubber block requiring frequent and costly replacement of the elastomeric components.
Track pads for shoes presently are made from styrene-butadiene rubber (SBR). The widespread use of SBR in track pad applications appears to be based on cost, historical precedent and the fact that at times the United States Government has required that the materials useed in their devices be available from sources within the United States to insure a continued supply. These factors in many ways are detrimental to the policy of continuing to use natural rubber for track pads and some shoe components, particularly since natural rubber is not available within the United States. Therefore, it is of the utmost importance to develop and use improved synthetic rubbers to improve the performance of tank track pads and shoes.
To improve field or service performance of tank pads, one must first identify those properties that are most needed and then optimize these. This is by no means a trivial task. Those skilled in the art would agree that to improve performance of pads and shoes, properties such as cutting and chipping resistance, tear and tensile strength, crack growth resistance, abrasion resistance, hysteresis and thermomechanical stability all have to be improved.